Effect of GM1 ganglioside on neonatally neurotoxin induced degeneration of serotonin neurons in the rat brain

Gangliosides attenuate stress-induced changes on body weight, motor activity and on the behavioral response to 5-methoxy-N,N-dimethyltryptamine

The major goal of this study was to evaluate the influence of gangliosides (GANG) treatment on the onset of adaptive changes and the sequelae induced by stress exposure. With this purpose, the behavioral response to 5-methoxy-N,N-dimethyltryptamine (5-MeODMT, 5 mg/kg, IP) and motor activity were evaluated in rats previously submitted either to a single restraint session (2 h) or to a daily restraint event for 3 consecutive days, combined or not to GANG administration (30 mg/kg IP). GANG was always injected 2 h before stress exposure. In addition, differences in body weights were recorded throughout the experiments. A similar behavioral response after 5-MeODMT was observed between saline (SAL) and GANG unstressed rats. Exposure to one or three restraint sessions did not modify the behavioral response to 5-MeODMT, whereas the association of GANG and stress during 3 consecutive days enhanced forepaw treading and hindlimb abduction. SAL-treated animals submitted to a single or to three stressful stimuli showed reduced locomotion and rearing. The combination of GANG and stress for 3 days, but not after a unique association, reversed the decrease on motor activity induced by the aversive experience. The decrease of body weights produced by one or three stress sessions was recovered only in animals treated with GANG and stress for 3 days. These findings suggest that GANG may accelerate the onset of adaptive changes on 5-HT1 sites and attenuate certain sequelae induced by previous stress experience.

Perinatal morphine treatment inhibits pruning effect and regeneration of serotoninergic pathways following neonatal 5,7-HT lesions

Lesion of the serotoninergic system in neonate rats is an ideal model for assessing the activity of chemical substances capable of affecting neuronal plasticity and regeneration (Jonsson et al., Dev Brain Res 16: 171-180, 1984). Treatment of newborn rats within 6 hr from birth with the selective neurotoxin 5,7-dihydroxytryptamine causes degeneration of the most distal serotoninergic axons. In our experimental conditions we have observed that after such neurotoxic treatment there is spinal cord denervation, which is particularly remarkable in the lumbar segment. This degenerative event is followed by gradual regeneration of the lesioned axons, with good reinnervation of the entire cord within 8 weeks. The degeneration-regeneration process is correlated with a transient hyperinnervation of the pons-medulla and hypothalamus by the short collaterals (pruning effect), as evidenced by increased serotonin content. Perinatal morphine exposure markedly impairs serotonin regeneration in the spinal cord. In addition, opiate treated rats are more susceptible to lesions, as shown by the neurotoxin induced denervation of the cortex, pons-medulla, and hypothalamus, which does not occur in lesioned controls. Therefore, our observations suggest that perinatal exposure to morphine affects the plasticity and regeneration of the developing serotoninergic system by increasing its susceptibility to neurotoxic lesions and reducing its regenerative capacity.

Sialyl cholesterol enhances the development of grafted neurons and motor recovery

Trophic actions of alpha-sialyl cholesterol (SC) and its sialidase-tolerant derivative, alpha-(3 beta-hydroxysialyl) cholesterol (SCt), were carried out on the development of midbrain neurons both in vitro and in vivo transplantation studies. Low to moderate concentrations of SC (0.01 to 0.05 micrograms/ml) facilitated neurite extension but had no effects on cell survival of primary cultured midbrain neurons. However, high concentration of SC (0.1 micrograms/ml) disturbed both neurite genesis and cell survival. SCt had a similar effect on midbrain neurons. At higher concentrations, SC and SCt induced concentration-dependent morphological changes in astrocytes from flat to fibrous. The effect on astrocytes was stronger in SCt than SC. At highest concentration tested (20 micrograms/ml), the proliferation of astrocytes was completely blocked, cells became detached and finally died. This effect of SC and SCt was partially blocked by simultaneous application of aFGF. Following dopaminergic cell grafting in vivo, SC and SCt had biphasic effects: a low dose (0.2 mg/kg, SC) enhanced motor recovery at 4 and 6 weeks after transplantation, while the highest dose (20 mg/kg, SC) disturbed motor recovery at all periods tested. These effects on motor recovery were paralleled by an effect on neurite genesis as studied by tyrosine hydroxylase immunostaining. Thus, at low concentrations, SC and SCt are neurotrophic agents that stimulate the development and differentiation of dopaminergic neurons.

Effects of GM1 ganglioside upon neuronal degeneration during withdrawal from alcohol

In previous studies we demonstrated that chronic alcohol consumption induced hippocampal cell and synapse loss in offset with an increase in the length of granule cell dendrites. In addition we observed that withdrawal after long periods of alcohol intake worsened the degenerative processes and that dendritic alterations were no longer apparent. In an attempt to reverse these structural changes we tested the action of GM1 ganglioside during the withdrawal period as there is evidence that GM1 may enhance neuronal recovery after different kinds of brain lesions. Cell and synaptic quantifications were performed and the branching pattern of the granule cell dendritic arborizations was analysed. The number of dentate granule and CA3 pyramidal cells from GM1-treated animals was found not to be significantly different from that of the alcohol-treated and withdrawal groups. No quantitative changes were found in the number of mossy fiber-CA3 pyramidal cell synapses when the aforementioned groups were compared. Whether the lack of effectiveness of GM1 can be related to the model employed or not is thoroughly discussed.

Stereotaxic injection of GD1a ganglioside induces limited recovery of striatal dopaminergic system in MPTP-treated aging mice

The systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to young (2 months old) and aging (12 months old) C57BL/6 mice (4 x 20 mg/kg i.p. given 12 hr apart) reduced tyrosine hydroxylase (TH)-immunoreactive (IR) fibers in the striatum and reduced dopamine (DA) concentration to 35% of controls in young and 22% of controls in aging mouse brain 5 weeks after administration. Stereotaxic injection of GD1a ganglioside (3 x 100 micrograms, 5 days apart) into the striatum of MPTP-treated young mice restored striatal DA concentration to 52% of the control concentration 5 weeks after MPTP injection. Similar injections of GD1a ganglioside restored striatal DA concentration of MPTP-treated aging mice to only 31% of the control concentration. Immunocytochemical analysis showed significant recovery of TH-IR fibers in the striatum of MPTP-depleted young mice treated with GD1a ganglioside, while TH-IR fibers in the striatum of MPTP-depleted aging mice treated with GD1a ganglioside showed less recovery. We conclude that treatment of MPTP-depleted aging mice with GD1a ganglioside results in more limited recovery in the nigrostriatal DA system than in young mice.

tGS ganglioside induces peculiar morphological features in grafted dopaminergic cells and promotes motor recovery in rats with unilateral lesions in the nigrostriatal dopamine pathway

A cell suspension of substantia nigra from fetal rats was introduced into the ipsilateral caudate nucleus of rats with unilateral lesions in the nigrostriatal dopamine pathway, and effects of bovine total ganglioside (tGS) and monosialoganglioside (GM1) treatment on the morphological features of the transplanted cells and recovery from motor imbalance (rotation induced by methamphetamine) were investigated. Gangliosides (30 mg/kg) were administered intraperitoneally once a day for 2 weeks after transplantation to test animals while control animals received saline alone. tGS animals showed definite motor recovery in the 2nd week (P less than 0.05) while control and GM1 animals exhibited slight recovery only. At 6 weeks after transplantation, motor imbalance disappeared in all 3 groups. Tyrosine hydroxylase (TH) immunocytochemical staining revealed that in the 2nd week TH-positive cells in tGS animals had more primary dendrites and more large neurites (meganeurites) than did controls. TH-positive cells of all 3 groups often had spiny processes at that time. In the 20th week, TH-positive cells became more multigonal and had wider dendritic fields in all groups, and had less meganeurites and spines. Motor recovery of each animal was dependent on the number of TH-positive cells and no significant difference was observed in the number of TH-positive cells among the three groups. tGS treatment for 2 weeks without grafting induced immunohistologically no axonal sprouting in the substantia nigra, medial forebrain bundle, accumbens and caudate nucleus when the chemical lesions were complete. Data suggest that tGS induces hypertrophy but not hyperplasia of the transplanted nigral cells, and increases the morphological plasticity. This might be the basis for promotion of recovery in motor function after transplantation.

Gangliosides prevent MPTP toxicity in mice--an immunocytochemical study

The role of gangliosides in preventing neuronal degeneration was examined in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse parkinsonian model. Intraventricular injections of a ganglioside mixture prior to MPTP treatment reduced MPTP's toxicity on tyrosine hydroxylase-positive neurons in the substantia nigra. This raises the interesting possibility that early ganglioside administration may be beneficial in the treatment of neurodegenerative disorders.

Hypoxia-induced neurotransmitter deficits in neonatal rats are partially corrected by exogenous GM1 ganglioside

Exposure of 7-day-old rats to 7% oxygen/balance nitrogen for 2 h results in selective changes of cholinergic, serotonergic, and dopaminergic neuronal markers in the frontal cortex, hippocampus, and striatum when evaluated 3 weeks after the insult. There is also about a 15% deficiency in brain weight. Treatment with GM1 ganglioside, 50 mg/kg i.p., for 2 days before and for 3 weeks after the hypoxic insult partially corrects the neurodevelopmental abnormalities including the deficiency in brain weight. We conclude that GM1 ganglioside might have therapeutic potential for treating suspected neonatal hypoxia.

Ganglioside GM1 prevents and reverses toluene-induced increases in membrane fluidity and calcium levels in rat brain synaptosomes

The effects of exposure to ganglioside GM1 and to toluene in vitro upon synaptosomal integrity have been examined using fluorescence polarization of two probes: 1-[4(trimethylamino)phenyl]-1,3,5-hexatriene (TMA-DPH) and 1,6-diphenyl-1,3,5-hexatriene (DPH) to measure membrane anisotropy, and the fluorescent indicator fura-2 to assay levels of cytosolic calcium [( Ca2+]i). The anisotropy of both TMA-DPH and DPH was decreased by toluene, implying increased membrane fluidity. The decrease in TMA-DPH but not in DPH anisotropy was prevented by pretreatment with GM1 in concentrations as low as 10 microM. This is not an additive interaction since 10 microM of GM1 alone did not significantly modulate TMA-DPH anisotropy. When the GM1 treatment succeeded the addition of toluene the decrease in anisotropy of both probes was reversed. Toluene treatment increased [Ca2+]i in a dose- and time-dependent manner. This increase could partially be both prevented and reversed by treatment with 50 microM of GM1. These effects may reflect an additive interaction, since this concentration of GM1 alone reduced [Ca2+]i. The present results show that toluene increases membrane fluidity and intracellular calcium levels. These effects may be counteracted by the endogenous compound GM1.

Exogenous GM1 gangliosides induce partial recovery of the nigrostriatal dopaminergic system in MPTP-treated young mice but not in aging mice

The administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to young (2-3 months) and aging (12 months) C57BL/6 mice (4 x 20 mg/kg, i.p., given 12 h apart) reduced tyrosine hydroxylase (TH)-immunoreactive (IR) fibers in the striatum, and reduced dopamine (DA) concentration to 28% of controls in young, and 16% of controls in aging mouse brain five weeks after administration. Although GM1 ganglioside treatment (30 mg/kg, i.p., daily for 5 weeks) restored striatal dopamine concentration to 74% of the control concentration in young mice, such an apparent recovery was not seen in aging brain. Immunocytochemical analysis also showed marked recovery of TH-IR fibers in the striatum of MPTP-depleted young mice treated with GM1 ganglioside while TH-IR fibers in the striatum of MPTP-depleted aging mice showed no recovery with such treatment. We conclude that treatment of MPTP-depleted young mice with GM1 ganglioside results in partial recovery in the striatal DA system, but such benefits do not extend to aging mice.

Denervation and hyperinnervation in the nervous system of diabetic animals. II. Monoaminergic and peptidergic alterations in the diabetic encephalopathy

The monoaminergic innervation of the central nervous system (CNS) is characterized by long and short projecting neurons. The neurological correlates of diabetes are usually referred to as processes of degenerative atrophy affecting motor and sensory peripheral nerves. We have found that the long serotoninergic axons innervating the spinal cord and the cerebral cortex are unaffected in diabetic animals and that the noradrenergic innervation of the cortex is normal as well. The serotonin content is doubled in the hypothalamus with no apparent alteration of 5-HIAA levels, suggesting a supernumerary innervation that is accompanied by a reduced release. In pons medulla oblongata, serotonin and dopamine with the relative metabolites 5-HIAA and DOPAC are significantly reduced, whereas noradrenaline is markedly increased. In the hippocampus, there is a reduction of serotonin content. The serotoninergic alterations are peculiar as suggested by the sparing of the most distal projections that is accompanied by hyperinnervation of the hypothalamus and the loss of shorter collaterals in the pons medulla oblongata. In the hypothalamus and in the striatum of diabetic rats, there are significant higher levels of substance P and met-enkephalin, respectively. The abundance of proenkephalin A mRNA is also increased in the striatum. Conversely, in the lumbar cord of diabetic animals, the levels of substance P and met-enkephalin are significantly reduced. Such alterations likely reflect retrograde degeneration of the peripheral sensory input. The CNS changes are unlikely due to vascular abnormalities in the brain of diabetic rats; rather, we suggest that the persistent lack of insulin is the major factor involved as a trigger of the monoaminergic changes in the diabetic brain.

GM1 ganglioside-induced recovery of nigrostriatal dopaminergic neurons after MPTP: an immunohistochemical study

The administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mice results in the loss of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) from the mouse striatum and a loss of cells containing tyrosine hydroxylase (TH)-immunoreactivity from the substantia nigra. The cells that remained in the nigra after MPTP treatment were smaller in diameter than normal cells. Treatment with GM1 ganglioside beginning 24 h after establishing the MPTP lesion resulted in partial restoration of DA and DOPAC content in the striatum and an increase in the diameter of the TH-immunoreactive nigra cells. It appears, therefore, that treatment of MPTP-intoxicated mice with GM1 ganglioside results in the partial restoration of both the biochemistry and morphology of dopaminergic neurons.

GM1 ganglioside counteracts cholinergic and behavioral deficits induced in the rat by intracerebral injection of vincristine

The intracerebroventricular injection of 0.5 mg of vincristine sulphate in adult male Wistar rats caused within 11 days the impairment of motor and reflexive behavior, evaluated by the elevated platform and hanging wire tests, a decrease in food consumption and loss of body weight, a 45% decrease in hippocampal choline acetyltransferase (ChAT) activity and a 35% decrease in the rate of high-affinity choline uptake (HACU) in the injected side. The latter effects are due to the death of neurons in the respective hemiseptum. Intrafimbrial injection of vincristine caused the same decrease in ChAT activity without behavioral alterations. Daily i.p. administration of GM1 ganglioside, beginning immediately after the vincristine injection, prevented dose dependently the decrease in ChAT activity and HACU rate. Prevention was complete with the 60 mg/kg dose. The same dose was equally active on ChAT activity when given s.c. but was inactive p.o. The ChAT decrease was also prevented when GM1 treatment began 5 days after vincristine. GM1 60 mg/kg i.p. also reduced the behavioral toxicity of vincristine. The possibility that GM1 might prevent vincristine toxicity by antagonizing its disruption of neurofilaments and axonal flow is discussed.

Interaction between nerve growth factor and GM1 monosialoganglioside in preventing cortical choline acetyltransferase and high affinity choline uptake decrease after lesion of the nucleus basalis

Monosialoganglioside GM1 and nerve growth factor (NGF) were administered alone or concomitantly to adult male rats with a unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (NBM). High-affinity choline uptake (HACU) rate and choline acetyltransferase (ChAT) activity were measured, 4 and 21 days after surgery, respectively, in the frontal and parietal cortices of both hemispheres. A 33-34% decrease in HACU rate and a 43-39% decrease in ChAT activity was found in the ipsilateral cortices 4 and 21 days, respectively, after the lesion. If the lesioned rats received NGF (10 micrograms i.c.v.) twice a week or daily administrations of GM1 (30 mg/kg, i.p.), beginning immediately after surgery the decrease in HACU rate and ChAT activity was smaller. If NGF and GM1 were given concomitantly no decrease in HACU rate and ChAT activity was detected in the lesioned hemisphere and a slight increase occurred in the contralateral hemisphere. However, after the concurrent administration of NGF (10 micrograms i.c.v.) and the inactive dose of GM1 10 mg/kg i.p. no decrease in HACU and ChAT activity was also found in the lesioned rats. The latter finding indicates a potentiation by GM1 of NGF effects on the cholinergic neurons of the NBM. The two drugs may either antagonize the neurotoxic effects of ibotenic acid or stimulate a compensatory activity in the remaining neurons.

Continued administration of GM1 ganglioside is required to maintain recovery from neuroleptic-induced sensorimotor deficits in MPTP-treated mice

Injection of a dose of haloperidol that has no obvious behavioral effects in normal mice, produces akinesia, catalepsy, and sensory neglect in MPTP-treated mice. Chronic GM1 ganglioside administration improves the behavioral impairments, partially restores striatal dopamine (DA) content and prevents DA D-2 receptor up-regulation. Discontinuation of GM1 ganglioside treatment results in a time-dependent decline of striatal DA content to pretreatment pathological levels, return of haloperidol-induced sensorimotor deficits and a rise of DA D-2 receptor density in the striatum. Apparently, continuous administration of GM1 ganglioside is necessary to maintain the biochemical and behavioral recovery in the MPTP-treated mouse. These observations may provide useful cues for understanding the mechanism of action of GM1 ganglioside.

Reversibility and prevention of intraspinal peptidergic loss caused by sciatic nerve lesions

We have investigated the reversibility and prevention of peptidergic losses in the lumbar spinal cord caused by permanent resection of sciatic nerve. The lesion triggers a series of degenerative events involving the substance P sensory imput as well as met-enkephalin interneurons of the substantia gelatinosa. The degenerative processes are evident 10 days after sciatic nerve lesion and are gradually reversible as shown by radioimmunoassay and quantitative immunocytochemistry. Recovery begins 30 days postlesioning and full restoration is observed at 90 days. Serotonin (5-HT) turnover is markedly affected by sciatic nerve lesion as soon as 24 hr postlesioning, when 5-HT metabolism is enhanced, returning to control levels just preceding the peptide alterations; 5-HT metabolism then undergoes a transient period of hypoactivity which correlates with the beginning of the peptidergic restorative processes. Altogether these results, with previous observations showing that 5-HT depletion prevents metenkephalin interneurons degeneration triggered by the lesion (Di Giulio et al.: J Neurosci Res 18:443-448, 1987), suggest a role for 5-HT in the synaptic plasticity of the substantia gelatinosa of the spinal cord. The administration of gangliosides (10 or 50 mg/kg) to sciatic-nerve-lesioned animals fully prevented the metenkephalinergic degeneration without affecting the degenerative atrophy of the lesioned substance P sensory imput.

Treatment with GM1 ganglioside restores striatal dopamine in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mouse

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 30 mg/kg i.p. daily for 7 days, was administered to mice. This dosage regimen resulted in an approximately 50% reduction of striatal dopamine (DA) level. Chronic administration of GM1 ganglioside (II3NeuAc-GgOse Cer), beginning between 1 to 4 days after terminating MPTP dosing, resulted in partial restoration of the striatal DA level. From dose- and time-response studies, it appeared that 30 mg/kg i.p. of GM1 administered daily for approximately 23 days resulted in an approximately 80% restoration of the DA level and complete restoration of the 3,4-dihydroxyphenylacetic acid (DOPAC) content. This dosage of GM1 also restored the turnover rate of DA in the striatum to near normal. Discontinuing GM1 treatment resulted in a fall of DA and DOPAC levels to values found in mice treated with MPTP alone. There was no evidence for regeneration of nerve terminal amine reuptake in the GM1-treated mice as evaluated by DA uptake into synaptosomes. Our biochemical findings in animals suggest that early GM1 ganglioside treatment of individuals with degenerative diseases of dopaminergic nigrostriatal neurons might be fruitful.

Exogenous GM1 gangliosides protect against retrograde degeneration following posterior neocortex lesions in developing hamsters

Developing and adult hamsters received unilateral neocortex aspiration lesions and were then treated daily with exogenous ganglioside (GM1, 30 mg/kg, i.p.). When lesions were made at the age of two weeks, GM1-treated animals had less shrinkage of the dorsal lateral geniculate nucleus of the thalamus compared to controls. Although a similar observation was made in adults, the effect was not as striking. Thus, GM1-treatment reduces retrograde degeneration after neocortical lesions and this effect is most pronounced during early development.

Endogenous levels of serotonin and 5-hydroxyindoleacetic acid in specific areas of the pigeon CNS: effects of serotonin neurotoxins

Endogenous levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined by high-performance liquid chromatography (HPLC) in specific regions of the pigeon central nervous system (CNS). High endogenous 5-HT levels in the visual wulst and brainstem and medium 5-HT content in the optic lobes were found. The cerebellum and retina showed low endogenous 5-HT levels. Similar endogenous 5-HIAA levels were measured in the visual wulst, optic lobes and brainstem, whereas the 5-HIAA content of the cerebellum and retina was significantly lower. The effects of para-chloroamphetamine (p-CA) and 5,7-dihydroxytryptamine (5,7-DHT) on the 5-HT and 5-HIAA content of the same regions were studied. Six days after p-CA treatment, the 5-HT content of the visual wulst, optic lobes, brainstem and the 5-HIAA content of the optic lobes and cerebellum markedly decreased. Nine days after 5,7-DHT administration, the 5-HT and 5-HIAA content of the visual wulst and optic lobes was significantly reduced. At longer survival times, serotonergic systems were differentially affected depending on both the neurotoxin treatment and the specific brain regions examined. The 5-HT content of the pigeon retina was not modified by p-CA treatment, whereas 5,7-DHT intravitreally injected caused a pronounced 5-HT depletion. Our results demonstrate that selective neurotoxins for serotonergic systems can provide a useful denervation tool for the study of serotonergic function in the pigeon CNS.

The role of ultrastructural investigations in neurotoxicology

The ways in which ultrastructural approaches have been applied to the investigation of xenobiotic-induced toxicity of the nervous system have been briefly reviewed. These approaches have been grouped in 3 broad areas, viz. morphology, function and composition. Firstly, morphological approaches permit the visualisation of changes in intercellular relationships, the identification of the subcellular target(s) of a xenobiotic substance and the discrimination between what may appear ostensibly to be identical cellular responses to one or more chemically distinct toxins. Secondly, functional approaches using, e.g. cytochemistry, ion precipitation, immunocytochemistry and autoradiography provide indications of metabolic state, the identity or the intra- or extracellular location of the "reactive species". Thirdly, those approaches, viz. electronprobe X-ray microanalysis and electron energy loss spectroscopy which provide information of the elemental composition of cells and tissues permit an assessment of the subcellular distribution and compartmentalisation of endogenous substances and toxic or therapeutic xenobiotics. In concert, ultrastructural approaches possess the ability to contribute unique information on the effects of exposure of cells of the nervous system to toxic substances and so direct further investigation towards an understanding of the mechanism of action.

GM1 ganglioside enhances synaptosomal resistance to chemically induced damage

A neurotoxic agent, chlordecone, damages the limiting membrane of isolated synaptosomes prepared from rat brain. This is shown by increased levels of free, ionic calcium and increased permeability of synaptosomes, using the fluorimetric probe, fura-2. Pretreatment of synaptosomes with the monosialoganglioside GM1, attenuates the effect of chlordecone. A parallel preincubation of synaptosomes with diasialoganglioside GD1A effects a similar mitigation of chlordecone-induced elevation of free calcium but does not prevent general membrane leakiness as assayed by escape of dye from synaptosomes. These data may underlie the known effect of gangliosides in enhancing neuronal regeneration after lesion induction.

Sprouting of striatal serotonin nerve terminals following selective lesions of nigro-striatal dopamine neurons in neonatal rat

The effects of neonatal intracisternal 6-hydroxydopamine (6-OHDA; 50 micrograms) treatment on striatal serotonin (5-HT) nerve terminals in rat have been characterized using histo- and neurochemical methods. The 6-OHDA lesion caused a 60% reduction of striatal dopamine (DA) concentration when analyzed in the adult stage, while 5-HT levels were increased by about 40% and 3H-5-HT uptake in vitro was increased by about 60%. Using computerized image analysis, a marked increase in 5-HT-like immunoreactive terminal density was found in both rostral (+200%) and caudal (+50%) striatum. Pretreatment with the DA uptake blocker amfolenic acid completely counteracted the 6-OHDA-induced alterations in both DA and 5-HT neurons in the striatum, while pretreatment with the noradrenaline uptake blocker desipramine had no significant effects. Regional analysis of 5-HT levels in the CNS after neonatal 6-OHDA treatment or the combined desipramine + 6-OHDA treatment showed no significant effect in any of the brain areas analyzed, apart from the observed 5-HT increase in striatum. It was furthermore observed that the striatal 5-hydroxyindoleacetic acid (5-HIAA)/5-HT ratio was decreased, while the 3,4-dihydroxyphenylacetic acid (DOPAC)/DA ratio was increased following the 6-OHDA lesion, indicating compensatory mechanisms in turnover of transmitters. These alterations were completely reversed after pretreatment with amfolenic acid. The present results support the view that the 5-HT hyperinnervation following neonatal 6-OHDA treatment is a collateral sprouting response induced by lesioning of the striatal DA neurons.

Spinal cord transplants permit the growth of serotonergic axons across the site of neonatal spinal cord transection

These experiments were designed to determine whether transplants of fetal spinal cord tissue into lesioned spinal cord in newborn rats provide a terrain that supports the growth of serotonergic (5-HT) axons across the site of the lesion. Although descending serotonergic axons can regenerate after chemical lesions in adult animals, they show little regrowth after surgical lesions. In newborn animals, 5-HT axons do not regrow after either chemical or mechanical lesions since the axotomized raphe-spinal neurons die. After partial spinal cord lesions made in developing animals, immature axons can take an aberrant route around the site of the lesion to reach normal target areas. Even these robust, late-growing, uninjured axons, however, are unable to grow through the site of the spinal cord lesion. Immunocytochemical labeling was used to determine if descending serotonergic axons grow into fetal spinal cord transplants, and whether these axons cross the transplant to reach spinal cord levels caudal to the lesion. Spinal cord transection at a mid-thoracic spinal cord level on the day of birth resulted in a dramatic decrease in 5-HT immunoreactivity caudal to the lesion by one day postoperative. 5-HT immunoreactivity caudal to the lesion was abolished by 5 days postoperative and did not return after acute or chronic (6 months) survival periods. When a transplant of fetal spinal cord tissue was placed into the lesion site, 5-HT axons were identified throughout the transplant. At spinal cord levels caudal to the transection and transplant, the serotonergic axons were identified in the host spinal cord in both the white and gray matter. This 5-HT innervation was not confined to spinal cord segments adjacent to the lesion site but extended to spinal cord segments as far as lower lumbar levels. The reinnervation of the host spinal cord caudal to the transection was far less than that seen in unlesioned adult rat spinal cord. Horseradish peroxidase (HRP) injected caudal to the transection and transplant, retrogradely labeled neurons within the medullary raphe nuclei. The HRP and 5-HT results both depended on apposition of the transplant with the rostral and caudal stumps of the host spinal cord; without such apposition, labeling was abolished. These results indicate that the presence of a transplant at the site of the neonatal lesion modifies the environment at the lesion site in such a manner as to support the elongation of identified axons across the site of the lesion and into the host cord caudal to the lesion.

Recovery of cortical acetylcholine output after ganglioside treatment in rats with lesion of the nucleus basalis

The changes in acetylcholine release from the cerebral cortex induced by a unilateral electrolytic lesion of the nucleus basalis and by a treatment with GM1 monosialoganglioside (30 mg/kg i.p. for 20 days) were investigated. Acetylcholine release was measured using the cortical cup technique in rats transected at midpontine level. In the lesioned rats treated with saline an ipsilateral 38% decrease in acetylcholine release was observed. GM1 treatment prevented the decrease and brought about a 30% contralateral increase. These results indicate that GM1 induces a functional recovery of the cholinergic neurons ascending to the cortex.

Gangliosides in the nervous system during development and regeneration

Gangliosides are present in nervous tissues of echinoderms and chordates, but the amounts and patterns differ widely. There are changes in the ganglioside contents of nervous tissues during development in most animals studied. To a large extent, regional differences and changes with development and degeneration in ganglioside composition reflect changing and different proportions of cellular types and subcellular organelles within the tissue. GM1 and GM4 are enriched in myelin; GD1a may be a marker for dendritic arborization. During regeneration of fish optic nerve and rat sciatic nerve there is an increased amount of ganglioside proximal to the regenerating axon tips, which may largely be a result of accumulation. This could provide a relatively large reservoir of ganglioside to become incorporated into the sprouting axolemma. Gangliosides added exogenously to growth medium can induce neuritogenesis of several types of neurons. The mechanisms of this action are unknown but may be related to nerve growth factor, microskeletal organization, membrane fluidity, and other factors. Gangliosides injected into young animals affect brain development, but further studies are required to determine these effects more specifically. Ganglioside administration increases the number of sprouts in regenerating peripheral nerves, but does not seem to accelerate axonal elongation. Parenterally administered gangliosides alter the recovery of brain tissue from a variety of types of lesions, and clinical trials are in progress to determine if they are of benefit in human neurological disorders. The biochemical mechanisms of these in vivo ganglioside effects are poorly understood, but may involve modulation of several enzyme systems as well as other properties of neural membranes, such as fluidity. It is possible that gangliosides may play similar roles and operate through some of the same mechanisms in developing and regenerating nervous tissues.

Treatment with GM1 ganglioside increases rat spinal cord indole content

Chronic treatment with GM1 ganglioside apparently increases serotonin metabolism in the spinal cord of control and hemitransected rats. Dopamine metabolism is stimulated below a hemitransection with GM1 treatment. These observations are consistent with reports that GM1 promotes regrowth of neurons after experimental lesions of brain.

GM1 ganglioside counteracts selective neurotoxin-induced lesion of developing serotonin neurons in rat spinal cord

The effect of exogenous monosialoganglioside GM1 on neurotoxin-induced lesioning of bulbo-spinal serotonergic neurons of newborn rats was studied by means of biochemical and immunocytochemical techniques. 5,7-dihydroxytryptamine (5,7-HT, a selective serotonin neurotoxin) treatment of newborn rats caused a pronounced reduction of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in the thoracic and lumbar spinal cord, while an increase of 5-HT and 5-HIAA was found in the pons medulla. These biochemical alterations were regionally correlated with similar changes in 5-HT nerve terminal density analyzed by image analysis. GM1 administration (30 mg/kg for 4 consecutive days) antagonized the reduction of 5-HT and 5-HIAA levels induced by 5,7-HT treatment in the lumbar spinal cord of 2-month-old rats, as well as the decrease of 5-HT nerve terminal density in both thoracic and lumbar spinal cord of 1- and 2-month-old rats. A minor counteracting effect of GM1 was found in the pons medulla where the neurotoxin induced an increase of 5-HT and 5-HIAA levels. These data support the hypothesis that GM1 may have a preventing action on retrograde degenerative processes following chemical lesion and/or a growth-stimulating effect on injured 5-HT neurons.

GM1 monosialoganglioside inner ester induces early recovery of striatal dopamine uptake in rats with unilateral nigrostriatal lesion

The experiments concerned the effect of parenteral administration of GM1 monosialoganglioside inner ester on the uptake of [3H]dopamine ([3H]DA) in synaptosomes prepared from the corpus striatum of rats with a unilateral lesion of the nigrostriatal pathway. In the animals treated with the ganglioside, starting on the 2nd day after lesion, the apparent Vmax of [3H]DA uptake (desipramine-insensitive) showed a marked recovery (from 10% to 33% of the controlateral side) as early as after 3 days of treatment, with no changes in the apparent Km values.